1. Field of the Invention
The present invention relates to a circuit device, and more particularly, it relates to a circuit device comprising a circuit element.
2. Description of the Related Art
In a circuit device included in an electronic instrument or the like, the exothermic density per unit volume has recently been increased due to downsizing densification and multi-functionalization. In recent years, therefore, a metal substrate having high heat releasability has been employed as the substrate for this type of circuit device so that circuit elements such as an IC (integrated circuit) and an LSI (large-scale integrated circuit) are mounted on the metal substrate, as disclosed in Japanese Patent Laying-Open No. 8-288605 (1996), for example. A structure obtained by forming a hybrid IC (integrated circuit) on a metal substrate is also known in general. The term “hybrid IC” denotes a circuit device obtained by collectively integrating circuit elements such as IC chips, capacitors, resistors etc. onto a single substrate.
FIG. 22 is a sectional view schematically showing the structure of a conventional circuit device disclosed in the aforementioned Japanese Patent Laying-Open No. 8-288605. Referring to FIG. 22, a resin layer 102 functioning as an insulating layer containing silica (SiO2) added as a filler is formed on a metal substrate 101 of aluminum (Al) in the conventional circuit device. An IC chip 104 is mounted on a prescribed region of the resin layer 102 through a bonding layer 103 of resin. Metal wires 105 of copper are formed on regions of the resin layer 102 separated from ends of the IC chip 104 at prescribed intervals through the bonding layer 103. The metal wires 105 and the metal substrate 101 are insulated from each other through the resin layer 102. The metal wires 105 and the IC chip 104 are electrically connected with each other through wires 106.
In the conventional circuit device shown in FIG. 22 the metal substrate 101 of aluminum is employed while the IC chip 104 is mounted on the metal substrate 101 through the resin layer 102, so that a large quantity of heat generated from the IC chip 104 can be released through the metal substrate 101.
However, the conventional circuit device shown in FIG. 22, wherein a thermal expansion coefficient of the resin layer 102 is smaller than a thermal expansion coefficient of the metal substrate 101, includes a problem, that is, the metal substrate 101 under the resin layer 102 is deformed in such a manner that it is warped when the metal substrate 101 expands due to the heat generated in the IC chip 104. As a result, the circuit device is disadvantageously deformed.
As a possible solution for the foregoing problem, a rigidity (Young's modulus) of the entire resin layer 102 can be increased so that the deformation of the metal substrate 101 under the resin layer 102 is controlled. However, when the rigidity (Young's modulus) of the entire resin layer 102 increased, a tangential stress generated between the metal substrate 101 and the resin layer 102 is accordingly increased when the metal substrate 101 expands due to the heat generated in the IC chip 104. As a result, the resin layer 102 is unfavorably easily peeled from the metal substrate 101.